When a subscriber roams from their home network onto a visited network then certain signalling needs to take place before the roaming subscriber can obtain network services including voice, SMS and data services. The visited network can determine that a subscriber is roaming from an IMSI broadcast from their user equipment (UE). The IMSI also provides the visited network with an indication of the identity of the home network of the subscriber and therefore determine if a roaming agreement exists between the two networks. The home network is notified of the roaming subscriber by receiving their IMSI from the visited network. The home network HLS/HSS is updated with this information and the IMSI is also added to the VLR of the visited network. Communications between the visited network and the home network take place using various network interconnects and these are also used to provide services to the subscriber.
Network interconnects are expensive to use and may have limited bandwidth. Such requirements may have large variations over the year but will need to be provisioned to cope with the highest expected demand (e.g. during holiday periods). Furthermore, roaming subscribers usually have limited services available when roaming than when they are on their home network (e.g. limited to voice, data and SMS). Specific home network services (e.g. traffic, weather, banking, multimedia applications, etc.) provided by IP multimedia subsystem, IMS, servers will typically be absent when roaming. Furthermore, the roaming subscriber will not usually be able to use similar services available to subscribers of the visited network.
Accounting data for the services provided by the visited network to the roaming subscriber also needs to be passed between the visited and the home network and reconciled. This may require regular batch file transfers between the network operators.
FIG. 1 illustrates schematically a system 10 for providing services to a UE 50 that is roaming. The subscriber using the UE 50 has a home public land mobile network (HPLMN) 20 and is roaming on to a visited public land mobile network (VPLMN) 30. The HPLMN 20 has a home subscriber server (HSS) 40 that contains a home location register (HLR). When the UE 50 registers with the VPLMN 30 then the HPLMN 20 is notified of the subscriber. The subscriber identity is recorded in the HLR. Activity and services provided to the UE 50 are reported to the HPLMN 20. Roaming traffic from the UE 50 traverses back to the HPLMN 20 using a serving gateway 60 on the VPLMN 30 communicating with packet data network (PDN) gateway 70 within the HPLMN 20. The VPLMN 30 records call, SMS and data volumes supplied to each subscriber whilst roaming and these are reported to the HPLMN 20.
FIG. 1a shows schematically current roaming procedures where Local Breakout is being implemented. FIG. 2 shows a further high-level schematic diagram of current certain aspects of roaming telecommunications systems. In particular, a call session control function (CSCF) 90 is shown within the home network 20. A proxy-CSCF 95 is shown within the visited network 30 and in communication with the CSCF 90. Such arrangements limit services provided to roaming subscribers and have high overheads. Therefore, there is required a method and system that overcomes these problems.